In October 2007 an interesting prediction of the biotic pump theory was confirmed, namely that natural forests should increase transpiration during droughts
(Saleska S.R., Didan K., Huete A.R., da Rocha H.R. (2007) Amazon Forests
Green-Up During 2005 Drought. Science 318: 612). Increased evaporation leads to intensification of the upwelling fluxes of moist air and of horizontal influx of moist air from the ocean, to offset the adverse effects of the drought.
Forests that do regulate the water cycle are expected to behave like this. This behaviour was confirmed with satellite data on leaf area index in Amazon forests during the 2005 drought.